Simulations of H2 sorption were performed in Cu-MOF-74, a recent addition to the M-MOF-74 series. Electronic structure calculations revealed that the Cu2+ ions exhibit an unusually low partial positive charge distribution in Cu-MOF-74, which is a direct consequence of the Jahn-Teller effect. This is in contrast to the charge environment for the metal ions in some of the other M-MOF-74 variants as determined in previous work [ Pham, T.; et al. J. Phys. Chem. C 2015, 119, 1078-1090 ]. Because of the low magnitude of the partial charges of the Cu2+ ions in Cu-MOF-74, this MOF displays the lowest H2 uptake and Qst values of the M-MOF-74 series, which is consistent with what was observed experimentally for H2 sorption in this series of MOFs. Control simulations of H2 sorption in a nonphysical Cu-MOF-74 variant were performed in which a set of calculated partial charges, appropriate for one of the other M-MOF-74 analogues, were used. These simulations utilize a much higher partial positive charge for the metal ions and, as a result, a different shape for the simulated H2 sorption isotherms was obtained compared to that using the normal force field. This shape was not representative of the experimental isotherm for Cu-MOF-74, and thus, confirms the notion that the electrostatic parameters on the metal ions are the key to understanding the H2 sorption behavior in this MOF. Examining the distribution of the induced dipoles and the Cu2+-H2 distance via simulated annealing and executing two-dimensional quantum rotation calculations have also verified that the H2-metal interaction in Cu-MOF-74 is the weakest in the M-MOF-74 series. This study shows the power of using computational modeling to explain certain experimental observables and trends in a series of MOFs.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): FIC/2010/06
Acknowledgements: This work was supported by the National Science Foun-dation (Award No. CHE-1152362). Computations were per-formed under a XSEDE Grant (No. TG-DMR090028) toB.S. This publication is also based on work supported byAward No. FIC/2010/06, made by King Abdullah Univer-sity of Science and Technology (KAUST). The authors alsothank the Space Foundation (Basic and Applied Research)for partial support. The authors would like to acknowledgethe use of the services provided by Research Computing atthe University of South Florida.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.